The chief objectives of this proposal are: 1) To measure the availability of oxygen within the lumen of the oviduct and uterus of the guinea pig throughout the estrous cycle and during early pregnancy, 2) To determine the morphological, physiological and metabolic factors primarily responsible for regulating intraluminal oxygen tension, and 3) To assess the significance of alterations in oxygen concentration with the reproductive tract to conceptus development and blastocyst implantation. Intraluminal pO2 will be measured in vivo in the oviduct by means of a micro oxygen-electrode and in the uterine lumen by means of a needle-electrodes. In order to gain a greater understanding of the morphological, physiological and metabolic factors which regulate the amount of oxygen present with the female reproductive tract, changes in oviductal and uterine pO2 will be correlated with endogeneous ovarian steroid hormone levels, blood flow, capillary permeability, oxygen consumption and morphology. Luminal pO2 will be modified by the administration of estrogen and progesterone. The effects of copper IUD's on intrauterine pO2 will be determined. The relationship between lumina pO2 and uterine and oviductal LDH activity will be determined.